Monopersulfate oxidation of Acid Orange 7 with an iron(III)-tetrakis(N-methylpyridinium-4-yl)porphyrin intercalated into the layers of montmorillonite and pillared clay

Abstract

A biomimetic catalyst, iron(III)-tetrakis(N-methylpyridinium-4-yl)porphyrin (FeTMPyP), was loaded into montmorillonite (Mt) and pillared clay (Pi). The catalytic activities of the prepared catalysts for the decolorization of Acid Orange 7 (AO7) in the absence and presence of humic acid (HA), a major component of waste water, were compared. Turnover frequencies (TOFs) for the FeTMPyP-loaded Pi (6.7–9.4h−1) were larger than those for the FeTMPyP-loaded Mt (2.9–3.3h−1), while decolorization for the FeTMPyP-loaded Mt was inhibited in the presence of HA (TOFs of 1.3–2.1h−1). These results can be attributed to the fact that the large expansion in basal spacing for the Mt permitted the catalyst to be eluted and HA to be inserted into the Mt layer. However, the levels of catalyst elution and the inhibition of AO7 decolorization by HA were significantly suppressed in the case of the FeTMPyP-loaded Pi catalyst, which was prepared using smaller OH/Al and Al/Mt ratios. These results indicate that the Pi is more suitable support for the FeTMPyP catalyst than the Mt.